1. Technical Field
The present invention is directed to improved drum brakes and, more particularly, to an improved drum brake having a drum, at least one brake pad for engaging the internal surface of the drum, an actuating device for forcing the brake pad into contact with the drum, the drum including at least two diagonal grooves formed in the braking wall of the drum, each of the diagonal grooves extending from generally adjacent the inner side of the braking wall outwards towards the outer edge of the braking wall in the direction opposite the rotation of the drum such that water and other liquids which end up within the drum are directed into the grooves and channeled outwards to exit the interior of the drum, thus generally preventing the retention of liquids within the drum.
2. Description of the Prior Art
There are two major types of brakes which are used on vehicles, the disc brake and the drum brake. Of the two, the drum brake has been used for far longer and is still used today due to its reliability, longevity, and the fact that it is less expensive than an equivalent disc brake. In fact, continued technological development of drum brakes has made drum brakes almost as effective as disc brakes in many situations, and drum brakes are particularly well-suited for use with tractor trailers and the like, due to the ability of the drum brake to dissipate excessive heat built up as a result of the stopping of such large, heavy vehicles.
Briefly, a drum brake generally includes a drum having a cylindrical outer wall which surrounds a pair of brake shoes controlled by a brake cylinder which force the brake shoes outwards to contact the inner or braking wall of the drum, thus slowing and eventually stopping the rotation of the drum due to the frictional contact between the brake shoes and the braking wall of the drum. Because of the heat generated by friction between the brake shoes and the drum, it is neither desirable nor possible to completely enclose the drum brake to prevent foreign objects from entering the drum, and thus it is quite common, especially during periods of precipitation, for foreign materials such as water, mud, or other solid materials such as sand and road salt, to enter the drum and be retained therein due to the centrifugal force caused by rotation of the drum on the axle. Of course, the entry and retention of any foreign objects within the drum brake can affect performance of the drum brake, but a particular problem exists with the entry of water into the interior of the drum brake, as it occurs quite often and furthermore because the properties of water cause the water to form a thin layer on the braking wall of the drum due to the centrifugal force applied thereto. When water is present within the drum, activation of the brake shoes to engage the braking wall of the drum does not provide nearly the amount of stopping power available when the interior of the drum is dry. This is because the brake shoes first engage the thin layer of water which resides on the surface of the braking wall, and as water is not compressible, the brake shoe cannot directly contact the braking wall of the drum and thus a condition known as “hydroplaning” occurs, as shown in FIG. 2. In fact, until sufficient heat is built up through friction to evaporate the water from the interior of the drum, this condition continues and therefore the stopping distance required to stop the drum brake-equipped trailer is greatly increased, sometimes even doubled. There is therefore a need for a device or apparatus which will generally prevent this dangerous hydroplaning condition within the drum brake yet will not significantly increase the cost or complexity of the drum brake or significantly reduce the reliability of the drum brake.
Therefore, an object of the present invention is to provide an improved drum brake which will reduce hydroplaning within the brake.
Another object of the present invention is to provide an improved drum brake which includes an outer circumferential wall, a braking mechanism mounted within the outer circumferential wall of the drum brake which includes pads which contact the inner braking surface of the outer circumferential wall, the inner braking surface further including two or more diagonal grooves having generally V-shaped or U-shaped cross-sectional shapes, the diagonal grooves extending across the entire width of the outer circumferential wall.
Another object of the present invention is to provide an improved drum brake in which the diagonal grooves include top beveled edges which will not bind against the brake pad during the braking process.
Another object of the present invention is to provide an improved drum brake in which the diagonal grooves act to channel water away from the interior of the drum brake and release the water into the area external of the drum brake in order to ensure that brake pad to braking wall contact is generally free of hydroplaning.
Another object of the present invention is to provide an improved drum brake in which the diagonal grooves are shallow at the inner ends thereof and progressively get deeper as they extend to the outer edge of the drum brake to further assist in the channeling of water away from the braking surface of the outer circumference wall while also preventing brake freeze, a common condition encountered with drum brakes which have been sitting in cold temperatures for an extended period of time wherein the brake pads become frozen in a pool of water, thus preventing rotation of the vehicle's wheel.
Finally, an object of the present invention is to provide an improved drum brake which is relatively simple and durable in manufacture and is safe, effective, and efficient in use.